Hunter is absolutely correct. Each civilization suits a different playstyle. I prefer the Byzantines myself because of their versatility (and I just like them historically). They have the capability to turtle or rush because of their variety of tech options, but they do not specialize in one area.

It all depends on how you play of course, but I would suggest learning with the Byzantines because of that versatility, and then trying out the other civilizations to see if one happens to suit you better.

"Those that move mountains begin by removing small stones."-Chinese Proverb

Pick Saracens, you can balance out a bad economy at the market. For the skilled player, the market can be turned into a substitute for a fast castle at 13 minutes and go on a rampage of his choice (Monks suggested)